Cytoskeletal elements in the airway epithelial cells of the rat will be investigated as the possible intracellular target sites for 03 and N02. In vitro organ maintenance systems will be used to a) facilitate control of in vitro exposure to 03 (0.2 to 0.8 ppm) or N02 (0.5 to 5 ppm) or cytoskeleton-active agents; b) measure the effects of these agents on permeability and cytoskeletal structure; and c) compare effects of the agents with those produced by 03 and N02 in order to determine whether their mechanisms of action may involve the same or related cytoskeletal components. The observed effects will be related to the amount of each gas retained by tracheal tissue. In vitro experiments will be paralleled by selected in vivo studies in order to seek in vitro-in vivo correlations. Preliminary observations suggest that the mechanisms of action of cytoskeleton-active drugs such as cytochalasin B, which destabilizes the cytoskeleton and increases permeability, may be similar to that of 03 and N02, which also increase permeability. Cytoskeleton-stabilizing drugs, such as phalloidin and kinetin, may antagonize the effects of these gases. In vitro organ maintenance systems permit controlled exposure of rat tracheal tubes in measurement of quantity of gas retained. Transmucosal flux will be measured by applying tracer molecules (99mTc-DTPA, 3H-dextran, 125I-BSA) to the tracheal mucosa and sampling at the serosal surface for appearance of label. Immunocytochemistry by light and electron microscopy will be employed to characterize various cytoskeletal components and their relation to transport through tight junctions or endocytic vesicles. Freeze fracture will be employed in morphometry of tight junctions. The purpose of this study is to identify mechanisms of increased respiratory epithelial permeability upon exposure to 03 or N03. An added benefit may be the validation of an in vitro system for testing toxicity of gasses and aerosols. Such a system might be used for human respiratory tissue maintained and exposed in vitro to aid in extrapolating animal data to man in assessing risk of human exposure.